View source for Cassiopeia Dwarf

{{short description|Galaxy in the constellation Cassiopeia}}
{{redirect|Andromeda 7|the star|7 Andromedae}}
{{Infobox Galaxy
| name = Cassiopeia Dwarf
| image = Cassiopeia Dwarf (PGC 2807155) Hubble WikiSky.jpg
| image_size = 250px
| caption =Cassiopeia Dwarf by [[Hubble Space Telescope|HST]]/[[WikiSky]]
| epoch = [[Epoch (astronomy)#Julian years and J2000|J2000]]
| type = dSph<ref name=Navabi/>
| ra = {{RA|23|26|31.0}}<ref name="ned">{{cite web
  | title=NASA/IPAC Extragalactic Database
  | work=Results for Cassiopeia Dwarf
  | url=http://nedwww.ipac.caltech.edu/
  | access-date=2006-11-30 }}</ref>
| dec = {{DEC|+50|41|31}}<ref name="ned" />
| dist_ly = {{cvt|2.45|Mly|Mpc|lk=on}}<!-- from distance modulus μ = 24.38 mag --><ref name=Navabi>{{cite journal|doi=10.3847/1538-4357/abdec1|title=The Isaac Newton Telescope Monitoring Survey of Local Group Dwarf Galaxies. IV. The Star Formation History of Andromeda VII Derived from Long-period Variable Stars|year=2021|last1=Navabi|first1=Mahdieh|last2=Saremi|first2=Elham|last3=Javadi|first3=Atefeh|last4=Noori|first4=Majedeh|last5=Van Loon|first5=Jacco Th.|last6=Khosroshahi|first6=Habib G.|last7=McDonald|first7=Iain|last8=Alizadeh|first8=Mina|last9=Danesh|first9=Arash|last10=Gozaliasl|first10=Ghassem|last11=Molaeinezhad|first11=Alireza|last12=Parto|first12=Tahere|last13=Raouf|first13=Mojtaba|journal=The Astrophysical Journal|volume=910|issue=2|page=127|arxiv=2101.09900|bibcode=2021ApJ...910..127N|s2cid=231698580 |doi-access=free }}</ref>
| z = {{nowrap|−307 ± 2 km/[[second|s]]}}<ref name="ned" />
| appmag_v = 12.9<ref name="ned" />
| absmag_v = −13.3 ± 0.3<ref name=Navabi/>
| size_v = {{nowrap|2.5{{prime}} × 2.0{{prime}}}}<ref name="ned" />
| constellation name = [[Cassiopeia (constellation)|Cassiopeia]]
| notes = [[satellite galaxy]] of the [[Andromeda Galaxy]]
| names = Andromeda VII, And VII, Cas dSph, [[Principal Galaxies Catalogue|PGC]] 2807155, 
{{nowrap|Cassiopeia Dwarf Galaxy}}<ref name="ned" /><ref name="simbad">{{cite simbad
  | title=NAME Andromeda VII
  | access-date=2010-03-06 }}</ref>
}}

The '''Cassiopeia Dwarf''' (also known as '''Andromeda VII''') is a [[dwarf spheroidal galaxy]] about 2.45 [[light-year|Mly]] away in the [[constellation]] [[Cassiopeia (constellation)|Cassiopeia]].<ref name=Navabi/> The Cassiopeia Dwarf is part of the [[Local Group]] and a [[satellite galaxy]] of the [[Andromeda Galaxy]] (M31). In the sky, it appears behind the [[Milky Way]]'s [[galactic plane]], and so it is [[interstellar reddening|reddened]] by 0.194 magnitudes.<ref name=Navabi/> With a luminosity of {{solar luminosity|{{val|1.8e7}}|link=y}} and a stellar mass of {{solar mass|{{val|19.73e6}}|link=y}}, it is the brightest and most massive of the Andromeda Galaxy's dwarf spheroidal galaxy satellites. It also has the highest [[metallicity]] out of all of them.<ref name=Navabi/>

The Cassiopeia Dwarf was found in 1998, together with the [[Pegasus Dwarf Spheroidal Galaxy|Pegasus Dwarf]], by a team of [[astronomers]] (Karachentsev and Karachentseva)<ref name="Pritzletal2005">{{Cite journal
 | bibcode=2005AJ....129.2232P
 | title=The Dwarf Spheroidal Companions to M31: Variable Stars in Andromeda I and Andromeda III
 | journal=The Astronomical Journal |date=May 2005
 | volume=129 | issue=5 | pages=2232–2256 | doi=10.1086/428372
 |author1=Pritzl, Barton J. |author2=Armandroff, Taft E. |author3=Jacoby, George H. |author4=Da Costa, G. S. |arxiv = astro-ph/0501083 | s2cid=9749493
 }}</ref> in [[Russia]] and [[Ukraine]]. The Cassiopeia Dwarf and the Pegasus Dwarf are farther from M31 than its other known companion galaxies, yet still appear bound to it by gravity. Neither galaxy contains any young, massive [[star]]s or shows traces of recent [[star formation]]. Instead, both seem dominated by very old stars, with ages of up to 10 billion years. The main period of star formation occurred around 6.2 billion years ago, and 90% of the star formation in the Cassiopeia Dwarf was done by 5 billion years ago.<ref name=Navabi/>

==See also==
* [[Andromeda's satellite galaxies]]

==References==
{{reflist}}

==External links==
* [https://web.archive.org/web/20060220024027/http://www.seds.org/~spider/spider/LG/and7.html '''SEDS''': Dwarf Spheroidal Galaxy Andromeda VII]
* {{WikiSky|name=The Cassiopeia Dwarf}}

{{Sky|23|26|31.0|+|50|41|31|2580000}}
{{Andromeda galaxy}}

[[Category:Dwarf galaxies]]
[[Category:Dwarf spheroidal galaxies]]
[[Category:Local Group]]
[[Category:Andromeda Subgroup]]
[[Category:Cassiopeia (constellation)]]
[[Category:Astronomical objects discovered in 1998]]